edison



(No Model.)

T. A. EDISON.

ELEGTRIG LAMP.

Patented Oct. 18,1881.

film/2507'.

077a (9mm.

@NITED STATES PATENT Cr mea.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY, ASSIGNOR TO THE EDISONELECTRIC LIGHT COMPANY, OF NEW YORK, N. Y.

ELECTRIC LAMP.

SPECIFICATION forming part of Letters Patent No. 248,418, dated October18, 1881. Application filed January 31, 1881. (No model.)

T 0 all whom it may concern Be it known that I, THOMAS A. EDISON, ofMenlo Park, in the county of Middlesex and State of New Jersey, haveinvented anew and useful Improvement in Electric Lamps; and I do herebydeclare that the following is a full and exact description of the same,reference being had to the accompanying drawings,and to the letters ofreference marked thereon.

This invention relates to the carbons used as the incandescingconductors in lamps for giving light by electrical incandescence; andits object is to render more stable these carbon filaments, to the endthat the life of the lamps may, on the average, be prolonged.

When carbon filaments are used for lighting by incandescence aphenomenon is found, to which may be applied the term electricalcarrying. This is an absolute carrying or moving of the carbon itselffrom the negative to the positive end of the carbon. This action seemsto be similar to that in galvano-plastic operations. The cohesion amongthe molecules ot' the carbon seems to be so weakened by the heat ofincandescence that the molecules, or a portion of them, are graduallymoved from one end to the other of the carbon. The amount of suchcarrying depends upon the resistance of the filaments, the degree ofincandescence, the electro-motive force between the clamping-electrodes,and the state of the vacuum. While its amount may vary with varyingconditions of these elements, it is the great cause of the ultimatedestruction of the carbons used in high vacuo, and if its degree andamount can be reduced a proportionate increase in the life of thecarbons is insured.

To this end the invention consists, generally, first, in arranglng thecarbons in the lamps so that the strongest portion thereof, or theportion containing the most material, or the portion having the leastresistance, shall be at the negative clamp; and, secondly, inconstructing a carbon having a greater mass of matter and lessresistance at one terminal than at the other, the matter graduallydecreasing and the resistance gradually increasing from one to the otherpole.

1n constructing such acarbon it is made of its fullestwidthatthenegative end,whenceitgradually tapers to the positive end. Thisconstruction gives a lower resistance and a lower incandescence at thenegative end, so that the carrying from such negative end by electricalaction is materially reduced, while the total resistance, candle-power,and economy of the carbon may remain the same, its duration or usefulperiod being lengthened proportionately to the reduction of carrying. Inpractice such carbons should be made so that the unit of incandescenceat the negative pole will be about eleven or twelve candle power, risinggradually to eighteen at the positive pole, the average of the carbon orits total lighting effect being about sixteen candle power under normalconditions.

It is evident that instead of carbons being made tapering from one poleto the other, as described, the same result may be produced by takingordinary carbons, uniform. in 'size throughout their length, andincreasing the mass of matter and conductivity of one side by a depositof carbon thereon, or soaking certain parts in a carbonizable solution,drying, and then recarbonizing.

It often happens that carbons intended to be of uniform size throughouttheir length are found to be defective upon one side-that spots or weakplaces there appear. Such may be utilized by placing them in the lamp sothat the defective side becomes the positive end of the loop, the otheror perfect side, having less resistance, being made the negative side.By so using such carbons their life or duration will not be materiallyshortened, as the inevitable carryingthen proceeds from the perfect tothe imperfect side.

In the drawings, Figure 1 represents a carbon made especially to carryout this invention, and Fig. 2 the same embodied in a lamp.

In this case the end N, intended for the negative end of the loop, ismade Wide and tapers gradually to the positive end P.

\Vhat I claim is 1. A carbon for an incandescing conductor for anelectric lamp, having one of its ends or portions of less resistance andgreater mass lamps, or the lamps in the circuit, so that the to ofmatter than the other, substantially as set more perfectside is thenegative portion, subforth. stantially as set forth.

2. A carbon for an incandescing conductor This specification signed andwitnessed this for an electric lamp, tapering from one end to 19th dayof January, 1881. the other. THOS. A. EDISON.

3. The method of utilizingdefective or spotty Witnesses: carbons forincantlescing conductors in electric H. WV. SEELY, lamps, consisting inarranging them in the ERNEST J. BERGGREN.

